Aromatic nitroso compounds as silver oxidizing agents



United States Patent AROMATIC NITROSO COMPOUNDS AS SILVER OXIDIZING AGENTS Vsevolod Tulagin, Binghamton, N. Y., assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application March 19, 1954, Serial No. 417,499

7 Claims. (CI. 95-88) The present invention relates to photographic'sliver bleaching baths, and more particularly to those in which the effective oxidizing agent is an aromatic nitroso compoun The metallic silver produced in the processing of light sensitive silver halide emulsions and which is not to be retained in the ultimate product is eliminated by oxidation to form products soluble in a silver halide solvent, such as hypo. Oxidizing agents almost always employed for this purpose are water soluble ferricyanides, particularly those of the alkali metals, such as sodium and potassium.

The ferricyanides are rather powerful oxidizing agents, and when used to process film, containing oxidizable organic molecules, often give rise to undesired color formation because of the effect they produce on such oxidizable molecules. The above objection is manifested in the case where the silver is oxidized in the presence of a color former utilized in producing dye images in color film. There has been a need, therefore, for silver oxidants which are not as powerful as ferricyanides but which are capable of readily oxidizing silver while displaying a selective action thereon, particularly where selectivity is required as in the processing of film in color.

Aliphatic and aromatic nitroso compounds and their modes of formation are disclosed in the literature. The aliphatic compounds are true oximes and I have found these to be completely inactive as oxidizing agents for silver. The aromatic compounds may be of the type:

CN=NO C-N=o The former are prepared by nitrosating a secondary arylamine and while they display some activity it is too slow for practical purposes.

The latter compounds prepared by nitrosating a tertiary arylamine, however, are highly active and yet more gentle than the ferricyanides when used in the presence of easily oxidized organic molecules. In other words, their action is substantially selective and, hence, they may be employed with less danger of originating colored oxidation products from said oxidizable organic molecules.

The utilization of the latter group of nitroso compounds as silver oxidants and bleaching baths containing the same constitute the purposes and objects of the present invention.

The aryl nitroso compounds, the use of which is contemplated herein, are of the benzene series, and they carry a true nitroso group, to wit, the grouping having in para-position thereto a tertiary amino group. The tertiary amino group apparently has the function of stabilizing the compounds as true nitroso compounds and of activating the nitroso group so as to facilitate its action on metallic silver. In this respect, the compounds differ from those of U. S. P. 2,625,477, granted January 13, 1953, which are p-nitroso phenols existing either in the form of the nitroso compound or in the form of an oxime. It is evident from the patent that the compounds thereof are produced by nitrosating a phenol rather than a tertiary amine, and it is this distinction which causes'applicants compounds to evince properties superior to those of the patent with respect to speed of oxidation and selectivity.

The substituents on the tertiary amino group of the nitroso derivative may be aliphatic, i. e., alkyl, such as methyl, ethyl, propyl and the like, hydroxyalkyl, such as hydroxyethyl, hydroxypropyl and the like, carboxyalkyl, such as carboxymethyl, carboxyethyl and the like, sulfo alkyl, such as sulfomethyl, sulfoethyl and the like, or aromatic of the benzene series, i. e., phenyl, toluyl, sulfophenyl, carboxyphenyl and the like. It is, of course, evident that difierent substituents may be present on one and the same nitrogen atom, such as, for instance, alkyl and hydroxyalkyl, phenyl and alkyl and the like. The only condition which the substituent groups must satisfy is that they be of sufiiciently low molecular weight that the nitroso compounds are soluble in aqueous acid solution. This would normally rule out aliphatic substituents containing more than four carbon atoms and aromatic radicals containing more than one benzene ring.

The nitroso derivatives may bear other substituents on the phenyl ring to which the nitroso group is attached as, for instance, hydroxy, alkyl, i. e., methyl, ethyl or the like, alkylsulfamyl, such as methylsulfamyl, ethylsulfamyl and the like, aryl sulfamyl, such as phenylsulfamyl and the like, alkoxy, such as methoxy, ethoxy and the like, p-hydroxyalkoxy, such as fi-hydroxyethoxy and the like. It is preferred that any such substituent appear in the 3- position, although this is not an essential requirement of the invention.

Examples of nitroso derivatives which I have found to be eminently suitable are:

The majority of the above compounds are known in the literature and in any case may be prepared by conventional procedures. Such procedure involves the addition of sodium nitrite to a cold aqueous acid solution of the selected tertiary arylamine. Tertiaryamines which may be used in this procedure to produce suitable nitroso derivatives but not necessarily thoseenumerated above are:

. Dimethylaniline Diethylaniline N-ethyl-N-(fl-hydroxy)ethylaniline Di-B-hydroxyethylaniline N-phenyl-N-methylglycine N-phenyl-N-ethyltaurine Diethyl-m-toluidine N,N-dimethyl-3-butylsulfonamidoaniline N,N-dimethyl-3-acetylaminoaniline l0. 3-N,N-dimethylaminophenol 11. 3-N,N-dimethylaminoanisole 12. N-methyl-N-phenylaniline 13. N-ethyl-N-(p-sulfo)phenylaniline 14. N-ethyl-(p-carboxy)phenylaniline The bleaching compositions containing the nitroso compound as the etfective oxidizing agent also contain an alkali metal bromide, such as potassium bromide, and an acid, preferably hydrochloric acid. These bleaching baths are compounded so as to have the following composition, in which parts are by weight unless otherwise stated:

Nitroso compound 5-15 parts. Alkali metal bromide 10-50 parts. Aci 8-25 parts by volume.

Water to make 1000 parts.

While the pH value may vary over a wide range, it is recommended that the quantity of acid used with the other specific components be varied to adjust the pH between a value of 5 to l.

The bleaching composition may be compounded from a nitroso derivative isolated as such from the reaction solution in which it is formed, or the reaction solution itself may be used for the bleaching composition. In the latter case, the reaction mixture is produced as follows.

The selected nitroso derivative in a quantity of .05 mol is added to 700 cc. of water containing 250 grams of ice, the water having been acidified with -25 cc. of concentrated hydrochloric acid. There is then added to this solution, with agitation, a solution of 3.5 grams of sodium nitrite in water. When the solution is to be used, it is warmed to 65 F.

The following examples will serve to illustrate theinvention, but it is to be understood that the invention; is not restricted thereto. The parts are by weight unless-otherwise stated.

Example I Parts p-Nitroso-dimethylaniline 10 Potassium bromide 'Water to make 1000 parts.

To the above solution there is added hydrochloric acid in an amount of 8-25 parts by volume, the amount selected being sutficient to give apH of 3.

Example 11 Parts p-Nitroso-diethylaniline 12 Potassium bromide 14 Water to make 1000 parts.

To this solution there is added a sutficient quantity of hydrochloric acid in the range of 8-25 parts by volume to give a pH of 4.

Example III The procedure is the same as in Example I, excepting that the nitroso compound is N,N-diethyl- 2-methylsulfonamido-4-nitrosoaniline.

Example IV The procedure is the same as in Example II, excepting that the nitroso compound is N-p-nitrosophenyl-N-methylglycine.

To this solution there is added with agitation a solution in 50 cc. of water of 3.5 grams of sodium nitrite. In a few minutes, when the first reaction is complete, grams of potassium bromide are introduced. Before using this solution, it is warmed to F.

Example VI The procedure is the same as in Example V, excepting that there is used .05 mol of p-nitroso-N-ethyl-N-(psulfo)phenylaniline.

It is understood, of course, that the compositions contemplated herein will be used in the same way and at the same point in the processing of photographic film as the commonly used ferricyanides are presently employed.

Various modifications of the invention will occur to operators in this field. Thus, it is to be understood that any p-nitroso derivative of the type embraced by the above general formula may be used, and particularly those listed above. I, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

I claim:

1. A photographic bleaching composition comprising an aqueous acid solution of a water soluble p-nitroso compound of the benzene series, said compound bearing in a position para to the nitroso group a tertiary amino group in which the nitrogen atom is substituted by radicals selected from the class consisting of aliphatic radicals containing not more than four carbon atoms and aromatic radicals of the benzene series, and an alkali metal bromide.

2. The composition as defined in claim 1, wherein the nitrogen atom of the tertiary amino group is substituted by a radical selected from the class consisting of alkyl, hydroxyalkyl, carboxyalkyl, sulfoalkyl, and a phenyl radical, and by a further radical selected from the class consifitirlig of alkyl, hydroxyalkyl, carboxyalkyl and sulfoa y 3. The composition as defined in claim 1, wherein for a liter of solution the components are present in the fol-' lowing proportions:

5-15 parts by weight of the p-nitroso compound 10-50 parts by weight of the alkyl metal bromide 8-25 parts by volume of the acid 4. The composition as defined in claim 3, wherein the acid is hydrochloric acid.

5. The composition as defined in claim 1, wherein the p-nitroso compound is p-nitroso-diethylaniline.

6. The composition as defined in claim 1, wherein the p-nlitroso compound is p-nitroso-N-alkyl-N-hydroxyethylam me.

7. The composition as defined in claim 1, wherein the p-nitroso compound is p-nitrosodi-(p-hydroxy)ethylaniline.

References Cited in the file of this patent UNITED STATES PATENTS 2,625,477 Sawdey Ian. 13, 1953 

1. A PHOTOGRAPHIC BLEACHING COMPOSITION COMPRISING AN AQUEOUS ACID SOLUTION OF A WATER SOLUBLE P-NITROSO COMPOUND OF THE BENZENE SERIES, SAID COMPOUND BEARING IN A POSITION PARA TO THE NITROSO GROUP A TERTIARY AMIONO GROUP IN WHICH THE NITROGEN ATOM IS SUBSTITUTED BY RADICALS SELECTED FROM THE CLASS CONSISTING OF ALIPHATIC RADICALS CONTAINING NOT MORE THAN FOUR CARBON ATOMS AND AROMATIC RADICALS OF THE BENZENE SERIES, AND AN ALKALI METAL BROMIDE. 